Cleaning a facade without damaging it: the complete guide
A dirty facade is a house that looks old and neglected: green moss, pollution marks, dirt at the base of the walls or near the downpipes. Cleaning your facade is perfectly possible as a DIYer, but you must choose your method well. A bad clean, especially at too high pressure, can irreparably damage the render, pebbledash or joints. Better, then, to think before acting.
Identifying your facade's cladding
The cleaning method depends above all on the material. A standard plaster or lime render, a sprayed pebbledash, natural stone, brick, wood or composite cladding are not all cleaned the same way. As a general rule, the softer and more porous the support, the gentler you must be. An unsuitable clean can scratch the stone, detach the pebbledash or make water penetrate behind the cladding.
The different cleaning techniques
- The broom and soapy water: the gentlest method, ideal for light dirt and fragile renders. Use a neutral detergent or diluted black soap.
- The pressure washer: effective on stubborn dirt, but dangerous. As a general rule, do not exceed 100 bar and keep the lance at least 30 cm from the wall.
- Cleaning with a soft brush and lime: for limestone and traditional renders, manual brushing respects the support better.
- Specific anti-green and anti-moss products: for walls exposed to the north or in shade, which go green quickly.
- Sandblasting or soda blasting: reserved for professionals for ingrained dirt, to be entrusted to a specialist.
The steps of a gentle clean
- Choose a dry, windless day: cleaning in rainy weather would be pointless, and the wind spreads the splashes onto the windows and the neighbours.
- Protect the fragile parts: windows, shutters, letterboxes and any exterior electrical sockets, with tarpaulins or plastic film.
- Start with a dry brushing to remove the soil and leaves accumulated at the base of the wall.
- Apply the soapy solution from the bottom upwards to avoid runs, leave it to act for a few minutes, then rinse from top to bottom.
- If you use a pressure washer, first test on a discreet area and keep a distance and a grazing angle so as not to detach the render.
- Rinse abundantly and let it dry before considering a water-repellent or antifungal treatment.
Cleaning the problem areas
Green moss stains are generally treated with a diluted antifungal product, left to act then rinsed. The rust marks running under metal elements (brackets, railings) may require a specific treatment. And if your facade has cracks, render chips or hollow areas, cleaning is not enough: you will first need to repair the support, ideally with a suitable patching compound.
How much does a facade clean cost?
Doing it yourself, cleaning an average facade only costs a few dozen euros: a pressure washer to hire (15 to 40 € per day depending on the model), an antifungal product (10 to 25 €) and a few accessories. If you prefer to delegate, professional facade cleaning generally ranges between 5 and 15 € per m² depending on the method and the height of the building, often with a treatment included. It is a relevant option for tall houses or heavily soiled facades, where specialist equipment makes all the difference.
The mistakes to avoid
- Pointing the high-pressure jet directly at the joints and edges: you gouge grooves into an already fragile support.
- Using acid or an aggressive detergent without testing it on a hidden area: it can discolour the stone and kill the surrounding vegetation.
- Cleaning a facade in poor condition, with render that is coming away: you will make the damage worse.
- Letting water infiltrate behind the joinery during cleaning: systematically protect the perimeter of the windows.
- Believing a single annual clean is enough: an antifungal treatment at the end of the season and a check of the downpipes prolong the result on a lasting basis.
After cleaning: protecting the facade
A clean facade gets dirty less quickly if it is protected. A water-repellent treatment, applied to clean, dry render or stone, prevents water from penetrating and limits soiling: allow about thirty euros to treat an average house, and renew every five to ten years depending on the product. For walls that go green quickly, an algicide product as a finish also lengthens the life of the result.
Cleaning your facade mainly requires measure: choose a method suited to the support, work in dry, windless weather, use the pressure sparingly and protect the fragile elements. A clean, treated facade means a more beautiful house, protection against damp and a value that is preserved. In case of doubt about a fragile support or ingrained dirt, a professional facade cleaner remains the safest solution.